[3/8] migration: Add VMSTATE_WITH_TMP

Commit Message

Dr. David Alan Gilbert Oct. 27, 2016, 3:32 p.m. UTC

From: "Dr. David Alan Gilbert" <[e-mail]>

VMSTATE_WITH_TMP is for handling structures where some calculation
or rearrangement of the data needs to be performed before the data
hits the wire.
For example,  where the value on the wire is an offset from a
non-migrated base, but the data in the structure is the actual pointer.

To use it, a temporary type is created and a vmsd used on that type.
The first element of the type must be 'parent' a pointer back to the
type of the main structure.  VMSTATE_WITH_TMP takes care of allocating
and freeing the temporary before running the child vmsd.

The post_load/pre_save on the child vmsd can copy things from the parent
to the temporary using the parent pointer and do any other calculations
needed; it can then use normal VMSD entries to do the actual data
storage without having to fiddle around with qemu_get_*/qemu_put_*

Signed-off-by: Dr. David Alan Gilbert <[e-mail]>
Reviewed-by: David Gibson <[e-mail]>
---
 include/migration/vmstate.h | 19 +++++++++++++++++++
 migration/vmstate.c         | 38 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 57 insertions(+)

Comments

Juan Quintela Feb. 13, 2017, 12:04 p.m. UTC | #1

"Dr. David Alan Gilbert (git)" <[e-mail]> wrote:
> From: "Dr. David Alan Gilbert" <[e-mail]>
>
> VMSTATE_WITH_TMP is for handling structures where some calculation
> or rearrangement of the data needs to be performed before the data
> hits the wire.
> For example,  where the value on the wire is an offset from a
> non-migrated base, but the data in the structure is the actual pointer.
>
> To use it, a temporary type is created and a vmsd used on that type.
> The first element of the type must be 'parent' a pointer back to the
> type of the main structure.  VMSTATE_WITH_TMP takes care of allocating
> and freeing the temporary before running the child vmsd.
>
> The post_load/pre_save on the child vmsd can copy things from the parent
> to the temporary using the parent pointer and do any other calculations
> needed; it can then use normal VMSD entries to do the actual data
> storage without having to fiddle around with qemu_get_*/qemu_put_*
>
> Signed-off-by: Dr. David Alan Gilbert <[e-mail]>
> Reviewed-by: David Gibson <[e-mail]>

My idea was to do the other way around.

But as you beat me with the idea.

Reviewed-by: Juan Quintela <[e-mail]>


Bascially what I created was a VMSTATE_SYNTHETIC() where the field value
is null.  You create a new get/put functions for the special values.


But looking for far away it is basically the same, I just preffered the
name O:-)

Later, Juan

Patch

diff --git a/include/migration/vmstate.h b/include/migration/vmstate.h
index d0e37b5..b404360 100644
--- a/include/migration/vmstate.h
+++ b/include/migration/vmstate.h
@@ -250,6 +250,7 @@  extern const VMStateInfo vmstate_info_cpudouble;
 extern const VMStateInfo vmstate_info_timer;
 extern const VMStateInfo vmstate_info_buffer;
 extern const VMStateInfo vmstate_info_unused_buffer;
+extern const VMStateInfo vmstate_info_tmp;
 extern const VMStateInfo vmstate_info_bitmap;
 
 #define type_check_2darray(t1,t2,n,m) ((t1(*)[n][m])0 - (t2*)0)
@@ -641,6 +642,24 @@  extern const VMStateInfo vmstate_info_bitmap;
     .offset     = offsetof(_state, _field),                          \
 }
 
+/* Allocate a temporary of type 'tmp_type', set tmp->parent to _state
+ * and execute the vmsd on the temporary.  Note that we're working with
+ * the whole of _state here, not a field within it.
+ * We compile time check that:
+ *    That _tmp_type contains a 'parent' member that's a pointer to the
+ *        '_state' type
+ *    That the pointer is right at the start of _tmp_type.
+ */
+#define VMSTATE_WITH_TMP(_state, _tmp_type, _vmsd) {                 \
+    .name         = "tmp",                                           \
+    .size         = sizeof(_tmp_type) +                              \
+                    QEMU_BUILD_BUG_EXPR(offsetof(_tmp_type, parent) != 0) + \
+                    type_check_pointer(_state,                       \
+                        typeof_field(_tmp_type, parent)),            \
+    .vmsd         = &(_vmsd),                                        \
+    .info         = &vmstate_info_tmp,                               \
+}
+
 #define VMSTATE_UNUSED_BUFFER(_test, _version, _size) {              \
     .name         = "unused",                                        \
     .field_exists = (_test),                                         \
diff --git a/migration/vmstate.c b/migration/vmstate.c
index 75922dd..6df65ca 100644
--- a/migration/vmstate.c
+++ b/migration/vmstate.c
@@ -918,6 +918,44 @@  const VMStateInfo vmstate_info_unused_buffer = {
     .put  = put_unused_buffer,
 };
 
+/* vmstate_info_tmp, see VMSTATE_WITH_TMP, the idea is that we allocate
+ * a temporary buffer and the pre_load/pre_save methods in the child vmsd
+ * copy stuff from the parent into the child and do calculations to fill
+ * in fields that don't really exist in the parent but need to be in the
+ * stream.
+ */
+static int get_tmp(QEMUFile *f, void *pv, size_t size, VMStateField *field)
+{
+    int ret;
+    const VMStateDescription *vmsd = field->vmsd;
+    int version_id = field->version_id;
+    void *tmp = g_malloc(size);
+
+    /* Writes the parent field which is at the start of the tmp */
+    *(void **)tmp = pv;
+    ret = vmstate_load_state(f, vmsd, tmp, version_id);
+    g_free(tmp);
+    return ret;
+}
+
+static void put_tmp(QEMUFile *f, void *pv, size_t size, VMStateField *field,
+                    QJSON *vmdesc)
+{
+    const VMStateDescription *vmsd = field->vmsd;
+    void *tmp = g_malloc(size);
+
+    /* Writes the parent field which is at the start of the tmp */
+    *(void **)tmp = pv;
+    vmstate_save_state(f, vmsd, tmp, vmdesc);
+    g_free(tmp);
+}
+
+const VMStateInfo vmstate_info_tmp = {
+    .name = "tmp",
+    .get = get_tmp,
+    .put = put_tmp,
+};
+
 /* bitmaps (as defined by bitmap.h). Note that size here is the size
  * of the bitmap in bits. The on-the-wire format of a bitmap is 64
  * bit words with the bits in big endian order. The in-memory format